Selection and modulation of high ordertransverse modesin vertical cavity surface emitting lasers

A theoretical proposal to double the pulse repetition frequency by alternated current modulation of two orthogonal high order transverse modes of a vertical cavity surface emitting laser (VCSEL) is presented. Static and dynamic characteristics of weakly index guided VCSELs in a multitransverse mode regime are analysed. An eecient model that takes into account all the transverse modes supported by the waveguide is developed. Mode partition noise in a current modulated VCSEL is studied taking into account the azimuthal degree of freedom. Diierent transverse modes can be excited with a probability that is numerically calculated. For high injection currents modes that are not favoured in the steady state can be the ones excited with higher probability. The excitation probability is similar for azimuthally orthogonal modes. This symmetry can be broken by selecting a particular high order transverse mode by using azimuthal dependent current prooling. This selection can be achieved over current ranges as wide as ten times the threshold current. Current modulation of this transverse mode is then analysed. Alternated current modulation of two orthogonal high order transverse modes is also studied. Alternated modulation of these modes can double the pulse repetition frequency obtained by modulating just one high order transverse mode, without increasing injected current density levels. This current induced spatial switching leads to high frequency beam steering in the laser azimuthal direction.